Migrate pubspec_schema to null safety (#83441)

packages/flutter_tools/test/src/pubspec_schema.dart

diff --git a/packages/flutter_tools/test/src/pubspec_schema.dart b/packages/flutter_tools/test/src/pubspec_schema.dart
index 6e5bace..e91a179 100644
--- a/packages/flutter_tools/test/src/pubspec_schema.dart
+++ b/packages/flutter_tools/test/src/pubspec_schema.dart
@@ -2,30 +2,35 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_tools/src/flutter_manifest.dart';
 import 'package:flutter_tools/src/globals_null_migrated.dart' as globals;
-import 'package:meta/meta.dart';
 import 'package:yaml/yaml.dart';
 
 import 'common.dart';
 
 /// Check if the pubspec.yaml file under the `projectDir` is valid for a plugin project.
-void validatePubspecForPlugin({@required String projectDir, @required String pluginClass, @required List<String> expectedPlatforms, List<String> unexpectedPlatforms = const <String>[], String androidIdentifier, String webFileName}) {
-    final FlutterManifest manifest = FlutterManifest.createFromPath(projectDir+'/pubspec.yaml', fileSystem: globals.fs, logger: globals.logger);
-    final YamlMap platformsMap = YamlMap.wrap(manifest.supportedPlatforms);
-    for (final String platform in expectedPlatforms) {
-      expect(platformsMap[platform], isNotNull);
-      expect(platformsMap[platform]['pluginClass'], pluginClass);
-      if (platform == 'android') {
-        expect(platformsMap[platform]['package'], androidIdentifier);
-      }
-      if (platform == 'web') {
-        expect(platformsMap[platform]['fileName'], webFileName);
-      }
+void validatePubspecForPlugin({
+  required String projectDir,
+  required String pluginClass,
+  required List<String> expectedPlatforms,
+  List<String> unexpectedPlatforms = const <String>[],
+  String? androidIdentifier,
+  String? webFileName,
+}) {
+  final FlutterManifest manifest =
+      FlutterManifest.createFromPath(projectDir + '/pubspec.yaml', fileSystem: globals.fs, logger: globals.logger)!;
+  final YamlMap platformsMap = YamlMap.wrap(manifest.supportedPlatforms!);
+  for (final String platform in expectedPlatforms) {
+    expect(platformsMap[platform], isNotNull);
+    expect(platformsMap[platform]['pluginClass'], pluginClass);
+    if (platform == 'android') {
+      expect(platformsMap[platform]['package'], androidIdentifier);
     }
-    for (final String platform in unexpectedPlatforms) {
-      expect(platformsMap[platform], isNull);
+    if (platform == 'web') {
+      expect(platformsMap[platform]['fileName'], webFileName);
     }
+  }
+  for (final String platform in unexpectedPlatforms) {
+    expect(platformsMap[platform], isNull);
+  }
 }